Method of producing yeast biomass

Abstract

The invention relates to use of a substrate comprising C5 compound-containing material, in the growth of Saccharomyces yeast or the production of a product of Saccharomyces yeast, wherein the C5 compound-containing material is: (a) C5 compound-containing material obtained from lignocellulosic hydrolysate; (b) C5 compound-containing material obtained from fermentation of lignocellulosic hydrolysate; or (c) a mixture of (a) and (b). The invention also relates to a method of producing Saccharomyces yeast biomass or a product of Saccharomyces yeast using the substrate, and to methods of producing ethanol comprising incubating Saccharomyces yeast produced by the use or method. The invention further relates to strains of Saccharomyces yeast suitable for the use or methods.

Description

FIELD[0001]The invention relates to a method of producing Saccharomyces yeast biomass or a product of a Saccharomyces yeast, substrates for growth of such yeast, to strains of Saccharomyces yeast, and use of the strains of Saccharomyces yeast in the production of yeast biomass, and yeast products such as ethanol. The invention has particular application for producing ethanol using Saccharomyces yeast and the invention is herein described in that context.BACKGROUND[0002]Ethanol is an increasingly important renewable fuel for transport, as well as being important as an industrial chemical and 2-carbon chemicals precursor. Ethanol is mostly produced via fermentation of hexose based sugars by Saccharomyces yeast. The hexose based sugars are typically obtained from crop plants in the form of hydrolyzed starches from corn, wheat, barley, sorghum, millet, cassava, sweet potato, rice etc., or from sugar cane and sugar beet. The hexose based sugars that are fermented are typically glucose, f...

AI Technical Summary

Benefits of technology

[0020]By employing strains of Saccharomyces yeast which are capable of utilizing xylose, and typically one or more other carbon compounds, the inventors have found that what was previously considered to be a waste product could be used as a substrate for growth of Saccharomyces yeast biomass and / or production of Saccharomyces yeast products. The ability of the Saccharomyces yeast to grow on xylose, as well as other carbon compounds, found in the substrate reduces the biological oxygen demand and hence the chemical oxygen demand of the substrate.

[0035]In one embodiment, the substrate is utilized by growing the Saccharomyces yeast on the substrate. Typically, the Saccharomyces yeast is grown aerobically on the substrate. In embodiments where the substrate comprises C5 compound-containing material obtained from fermentation of ligocellulosic hydrolysate, aerobic growth of the Saccharomyces yeast on the substrate allows carbon sources that were not converted into ethanol or extracted from the fermentation process to be effectively removed from the waste stream and converted into useful yeast biomass. This has the added advantage of reducing the chemical and biological oxygen demand of the substrate.

[0080]Strain V08 / 013,411 and strain V09 / 005,064 are capable of tolerating high levels of inhibitors in lignocellulosic hydrolysate and in the substrate. Strains V08 / 013,411 and V09 / 005,064 are also capable of growth in the substrate using xylose as a sole carbon source for growth.

[0109]The use of ammonia serves to adjust the pH of the lignocellulosic hydrolysate to a range suitable to support yeast growth and fermentation. In addition, ammonia provides a readily available, inexpensive nitrogen source for the yeast to utilize.

[0111]Also, high levels of calcium salts can cause downstream processing problems due to the ability of calcium salts to produce scale within boilers. In addition, avoidance of the use of calcium hydroxide, calcium carbonate or sodium hydroxide for pH adjusting the hydrolysate avoids the associated ionic inhibitory and osmotic stress produced by these ions. Further, by using ammonia in the pH adjusting of the hydrolysate, nitrogen is provided for Saccharomyces yeast propagation and fermentation.

[0122]A fifteenth aspect provides a method of reducing the biological oxygen demand of a substrate comprising C5 compound-containing material obtained from fermentation of lignocellulosic hydrolysate, comprising incubating a Saccharomyces yeast with the substrate under conditions which cause growth of the Saccharomyces yeast.

Problems solved by technology

In particular, C5 compound-containing material obtained from fermentation of lignocellulosic hydrolysate was considered to be a waste stream unsuitable for growth of Saccharomyces.

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